For purposes of the present invention the term "oil" is intended to include a wide variety of petroleum products such as engine oil, lubricating oil, diesel fuel, gasoline, etc. In the operation of virtually all engine powered marine vessels having inboard engines a wide variety of petroleum products are utilized in conjunction with engine operation. During operation of the engine or engines a certain quantity of engine oil can be lost through engine seals and into the bilge of the vessel. Regardless of how clean and how well cared for is the engine system of the vessel it is virtually always the case that at least a small amount of engine oil is lost into the bilge. This engine oil tends to coat all of the exposed surfaces in the bilge and can combine with other contaminants such as dust, certain marine life to develop a coating or buildup of oily residue in the bilge. Also, during operation of the engine and during servicing of the engine, small amounts of lubricating oil are frequently lost into the bilge and some fuels or fuel components also find their way into the bilge due to minute leakage thereof during prolonged engine operation.
Inboard engines, especially in larger marine vessels typically have power output drive shafts that extend through seals in wall surfaces of the vessel, especially the bottom and transom surfaces. These rotary shaft seals are almost always subject to a small volume of water leakage as the shafts are rotated during vessel operation. This water leakage will build up in the bilge of the vessel; consequently it must be periodically removed from the bilge and pumped overboard by means of bilge water discharge lines having orifice openings externally of the vessel's hull. For the reason that leaked oil continuously collects in the bilge and leaked water through the shaft seals also collects in the bilge the bilge water in marine vessels is virtually always contaminated with oil that it picks up from bilge deposits. In the past, bilge water pumping systems have been provided which operate automatically or by manual selection and which function to pump bilge water, even though contaminated with oil out of the bilge of the vessel and into the surrounding water. Very few marine vessels are provided with any facility for separation of the oil from the bilge water and preventing oil from being discharged from the bilge and into the surrounding water. Also, under circumstances where bilge water filters have been employed, these filters are typically of containing a significant volume of oil; consequently they are not typically capable of providing for lengthy unattended service so that oil leakage from the filters becomes a problem. Certain marine vessels such as shrimp boats, oil well surface vessels and the like may operate for several days or weeks without returning to shore. In the case of bilge water filtering systems it is desirable even under extended use of this nature to provide bilge water filtering systems having the capability of being replenished or restored so that the vessel is always provided with the capability for efficiently filtering oil from the bilge water and thus insuring that no oil or other such debris is pumped overboard by the bilge pump system. Especially when marine vessels are operational for extended periods of time it is desirable for bilge water filtering systems thereof to have high volume oil retaining capability to thereby maximize the periods of efficient filter use and minimize the frequency of filter changes as the vessel is being operated.